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Cardiovascular Research 1998 39(2):492-505; doi:10.1016/S0008-6363(98)00111-4
© 1998 by European Society of Cardiology
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Copyright © 1998, European Society of Cardiology

Overexpression of Gi-proteins precedes the development of DOCA-salt-induced hypertension: relationship with adenylyl cyclase

Josée Marcil, Jacques de Champlain and Madhu B Anand-Srivastava*

Department of Physiology, Faculty of Medicine, Groupe de Recherche sur le Système Nerveux Autonome, University of Montreal, Montréal, Québec, Canada H3C 3J7

* Corresponding author: Tel.: +1 (514) 343 2091; Fax: +1 (514) 343 2111

Objective: In the present studies, we have investigated if aorta, like heart from deoxycorticosterone acetate (DOCA)-salt hypertensive rats, (HR) also exhibit enhanced expression of G-protein levels and if these alterations occur before or after the development of blood pressure. Methods: Sprague–Dawley rats treated with DOCA-salt or vehicle for 1, 2, 3 and 4 weeks were used for these studies. The levels of inhibitory guanine nucleotide regulatory proteins (Gi{alpha}-2, Gi{alpha}-3) and Gβ proteins were determined by immunoblotting, whereas the levels of Gi{alpha}-2 and Gi{alpha}-3 and adenylyl cyclase type V enzyme mRNA were determined by Northern-blotting techniques. Results: The blood pressure was significantly increased in DOCA-salt-treated rats as compared to sham-operated rats after 2 to 4 weeks of treatment; whereas no change in blood pressure was observed after 1 week of treatment (prehypertensive state). However, the levels of Gi{alpha}-2, Gi{alpha}-3 and Gβ proteins and Gi{alpha}-2 and Gi{alpha}-3 mRNA were significantly enhanced in hearts and aorta from DOCA-salt treated rats after 1 week of treatment and remained elevated up to 4 weeks of treatment. In addition, the Gi-mediated inhibitions of adenylyl cyclase by Angiotensin II (Ang II) and C-ANF4-23 were also greater in DOCA-salt-treated rats as compared to sham-operated rats after 1 week and longer periods of treatments (2 to 4 weeks). On the other hand, the levels of Gs{alpha} were not altered up to 2 weeks of DOCA-salt treatment but significantly decreased in rats treated for 3 and 4 weeks. Furthermore, the stimulatory effects of guanine 5'-[{gamma}-thio]triphosphate (GTP{gamma}S), isoproterenol and forskolin on adenylyl cyclase were decreased in both hearts and aorta from DOCA-salt-treated rats after 1 to 4 weeks of treatment as compared to sham-operated rats. The mRNA levels of adenylyl cyclase, type V enzyme in hearts from DOCA-salt treated rats were significantly decreased after 3 and 4 weeks of DOCA-salt treatment but not in rats treated for 1 or 2 weeks. Conclusions: These results indicate that the enhanced expression of Gi{alpha}-2 and Gi{alpha}-3 precedes the development of blood pressure in DOCA-salt-induced hypertension. It can thus be suggested that the increased levels of Gi proteins and resulting decreased levels of cAMP may be one of the factors that contribute to the impaired cardiac contractility and increased vascular tone in DOCA-salt hypertension.

KEYWORDS C-ANF4–23, a ring-deleted analog of atrial natriuretic factor, C-ANF4–23 (des[Gln18, Ser19, Gln20, Leu21, Gly22] ANF4–23-NH2]; FSK, forskolin; ADA, adenosine desaminase; GTP{gamma}S, guanosine 5'-[{gamma}-thio]triphosphate; Gs, stimulatory guanine nucleotide regulatory protein; Gi, inhibitory guanine nucleotide regulatory protein; WKY, Wistar-Kyoto rats; SHR, spontaneously hypertensive rats


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